Thursday, 3 June 2010

Counter-irritation

The ancient and somewhat vague concept of counter-irritation persists, in various guises, right through to the recent past. Through their history, counter-irritants have been either chemical (eg. extracts of chillies, mustards and the like) or physical (eg cupping, ‘medical electricity’, or even the brief flirtation of medicine with moxa) in nature and aimed to distract the body in one way or another from pain or irritation. Like many practices from medicines darker past, it could be deeply unpleasant: the desired effects of counter-irritants varied from mild itching through to severe inflammation and blistering.

Sometimes, a counter-irritant might be applied remote from the source of the problem. For example, during an attack of angina most patients experience shooting pains radiating away from the centre of the chest – typically down the left arm. Thus, one view held that a counter-irritant applied to the arm would distract (or “short-circuit”) the pain arising from the heart. In other cases, irritants were applied closer to the source of discomfort. Using angina as an example again, it was not uncommon for physicians to apply a mustard plaster to the chest to try to counter the pain within, or to try to somehow draw the inflammation out to the surface (it’s all a bit vague from our now more rigid perspective). These attempts to alleviate pain could be quite severe; it was not uncommon, and quite intentional, for painful blisters to develop. Counter-irritants would probably have been applied as frequently as (and as a adjunct to) copious blood letting. Although the practice of bleeding is now all but forgotten, the ghost of counter-irritation still walks. For example, clutching a hot water bottle to alleviate period pain is probably a hanger-on from this way of thinking. Whether this practice has any real therapeutic value would be difficult to determine with confidence; but few would deny it is soothing in some way. Similarly, acupuncture can be thought of as a counter-irritant, and many argue that this is how this largely unproven fad “works” (perhaps without realising it) to provide relief from pain. Many of us would bite a knuckle or part of the hand to counter pain elsewhere, especially as children. Counter-irritation makes tantalising sense at the lower end of the pain spectrum.

Until relatively recently, authors of medical texts tried to explain the mechanisms of counter-irritation by warping contemporary knowledge of neurophysiology around the supposed efficacy of the approach. For example, at one time it was thought that nerve impulses from pathologically painful sites could be short-circuited in the spinal cord or brain somehow by nerve impulses from the site of application of a counter-irritant. It’s not entirely absurd. We have probably all experienced vaguely similar phenomena when, for example, we are too preoccupied with a task to notice that we have cut ourselves in a way that would ordinarily be painful. Stories abound of soldiers enduring stressful combat experiences, only to notice a bullet wound that would have felled them if they had just been on guard. One current and popular explanation for such events would be that the brain produces endogenous analgesic substances such as endorphins in such situations. This is where the realms of actual efficacy and placebo effects intersect in the Venn diagram of pain: placebo effects of treatments have been consistently shown to depend on production of endorphins as well. Ironically, acupuncture is often touted on the basis that it induces endorphin release, as if this provides some scientific authority to this largely pointless practice, rather than evidence that it is nothing more than a placebo. And that is why the “ancient tradition” of acupuncture has been consistently found to be no better than just prodding someone randomly with a toothpick (placebo), but better than doing nothing at all.

The idea that sensory impulses can be short-circuited is still with us. There are a variety of devices that can be used to electrically stimulate the spinal cord in the vague hope of achieving pain relief. Some devices are surgically implanted, and patients can control when and how electrical stimulation is delivered. Despite the cost of equipment (and its implantation) there is very little evidence that this technique isn't just a placebo. At present it is indistinguishable from quackery: small, poorly-conducted clinical trials and anecdotes.

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I am a university lecturer with an interest in pharmacology. I post here odd bits and pieces I come across delving into the history of modern pharmacology. It's just for fun, in case other people find such things interesting.
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